nahtameen
A London version of 'na meen' used to tell someone they're being an absolute knob. It's like when you're being a bit of a prat and you think you're the most important person in the universe.
'He said he'd beat me at the pub quiz. Nahtameen!'
'She kept bragging about her holiday like it was the best thing ever. Nahtameen!'
'He said he'd be the best in the class. Nahtameen!'